Intramedullary Rod With Spiraling Flutes

ABSTRACT

This invention relates generally to devices, systems and methods for the internal fixation of bone fractures, and particularly, to intramedullary fracture fixation devices such as those used in, for example, the treatment of long bone fractures. An IM rod preferably is provided with multiple curved sections in different planes preferably designed to conform with the long bones of a patient, both during insertion and in the rod&#39;s final position in the long bone. In addition, the overlap of portions of the curved sections results in a co-planar curvature of portions of the IM rod which assist in the insertion process by guiding the proper rotation of the IM rod as it is inserted into the bone. Spiraling flutes extending down the distal portion of the rod also assist in properly guiding and orienting the rod about its longitudinal axis during insertion such that the appropriate segment of the curved rod conforms with the appropriate portion of the long bone at the appropriate place.

FIELD OF THE INVENTION

This invention relates generally to systems for the internal fixation ofbone fractures, and particularly, to intramedullary fracture fixationdevices such as those used in, for example, the treatment of long bonefractures.

BACKGROUND OF THE INVENTION

Fractures of the long bones, such as the femur, are often treated withthe use of an intramedullary rod (“IM rod”) inserted into the medullarycanal of the affected bone. An IM rod, as is well known in the art,generally comprises an elongated rod along with associatedcross-members, such as screws or nails, including nailing devices withhelical blades. The IM rod typically includes various transverse holesto allow for the placement of these associated cross-members through theIM rod and into bone tissue in order to stabilize and hold together thefragmented bone segments. For instance, in the treatment of fractures inthe area of the neck and/or head of the femur, a cross-member can beinserted through the proximal portion of the IM rod, across thefracture, and then into the femoral head. For more distal shaft typefractures, locking screws can be placed through the IM rod and into bonetissue at appropriate locations to provide fixation of the bonefragments.

A technique for implanting intramedullary rods involves insertion of therod through a point that is lateral to the center-line of the medullarycanal, i.e. offset from the piriformis fossa. One of the many examplesof the use of this technique is illustrated in U.S. Pat. No. 3,433,220to Zickel. An osteotomy at the tip of the trochanter is made to createan entry site and a flexible reamer is utilized to carry out the reamingof the medullary canal while conforming to its basic anatomy. Becausethe location of the entry site is laterally offset from the axis of themedullary canal, an angled or curved opening is created between theentry site and the medullary canal.

Once the opening is made, an IM rod can be inserted through the entrysite and into the medullary canal. However, the insertion point of an IMrod in a laterally offset placement is the site of possible iatrogenicfractures because the curvature of the opening into the medullary canal“angles” the rod into the medullary canal of the femur. This causes thepotential for fracture due to the inadvertent application of transversepoint loads against the bone. Fractures have been observed beginning atthe entry site and extending through the intertrochanteric regionfollowing IM rod insertion.

In addition, the shape of the medullary canal of the femur itself cancomplicate the insertion of an IM rod. The medullary canal has a gentle,uniform, anterior bowing throughout its length. If the IM rod does notpossess an anterior bend or curvature, transverse point loads may actagainst the cortical wall of the femur leading to fracture. Over-reamingthe medullary canal can prevent fracturing of the shaft duringinsertion, but this results in a decrease of the surface area contactbetween the rod and the bone, leading to less effective fixation of thebone fragments. Another detrimental effect of over-reaming is a decreasein the bending and torsional strength of the bone. As a result, many IMrods have anterior bends or curves in the anterior-posterior plane tomatch the normal medullary anatomy of the femur, as exemplified in theprior art by patents such as U.S. Pat. No. 3,433,220 to Zickel and U.S.Pat. No. 4,135,507 to Harris.

However, curvature of the rod in the anterior-posterior plane alone doesnot necessarily overcome the difficulties arising from the insertion ofthe IM rod through the laterally offset entry site. Additional sidepoint loads may be imposed on the bone by the proximal segment of the IMrod once the rod is in its final position because the anterior curvatureof the rod is in an orthogonal plane to the curvature of the openingbetween the entry site and the medullary canal. This may also result insubsequent fracturing of the femur. As a result, some IM rods (such asdisclosed in the prior art Zickel and Harris patents) have incorporateda bend or curve in the lateral-medial plane that attempts to conformwith the opening from the entry point into the medullary canal.Nevertheless, these laterally curved rods have not been completelysuccessful in eliminating inadvertent fracturing during the insertion orremoval procedure.

When an IM rod is provided with an anterior curve, rotating the rodapproximately 90 degrees about its longitudinal axis prior to insertionmay facilitate its insertion into the medullary canal because the rod'scurvature could more closely approximate the curvature of the openingbetween the entry site and the medullary canal. Thus, the rod isinitially inserted in this rotated orientation and then twisted as it isdriven into the medullary canal to its final position. However, applyingthe proper amount of twisting force at the appropriate time isproblematic as it may be difficult to continuously monitor the preciseextent of the rod's progress into the medullary canal while alsoapplying the corresponding amount of twist required at each point. Inaddition, IM rods are often provided with external flutes extendingstraight down the surface of the shaft of the rod that may interferewith this twisting motion during insertion. While these external flutesare desirable because they provide benefits such as improved medullaryrevascularization, reduced stiffness with greater strength, and improvedtorsional fixation at the rod-bone interface, the engagement of theflutes with bone inside the medullary canal may actually impede thetwisting necessary in order to insert the rod.

SUMMARY OF THE INVENTION

The IM rod of the present invention preferably provides a rod withmultiple curved sections in different planes designed to conform withthe curvature or bend of the long bone in which it is inserted, bothduring insertion and in the rod's final position in the long bone. Inaddition, the multiple curved sections in different planes may overlapresulting in a co-planar curvature of portions of the IM rod whichassist in the insertion process by guiding the proper rotation of the IMrod as it is inserted into the bone. Spiraling flutes extending down thedistal portion of the rod also assist in properly guiding and orientingthe rod about its longitudinal axis during insertion such that theappropriate segment of the curved rod conforms with the appropriateportion of the bone at the appropriate location.

The IM rod comprises an elongated rod with a proximal head, a distalstem and transverse holes preferably provided at a variety of locationsalong its length to accept cross-members, thus allowing effectivefixation of a number of different types of fractures. The rodadditionally may comprise at least two non-tangential (i.e. nottouching) curved sections in the lateral-medial plane, and preferably atleast a third curve in the anterior-posterior plane. The stem mayinclude flutes that extend down the surface of the rod and preferablytwist approximately 90 degrees about the longitudinal axis of the rod.Various cross-members such as, for example, screws, bolts, nails, and/ortacks may be provided for insertion through the transverse holes andinto bone tissue.

Prior to insertion into the femur, the rod is rotated about itslongitudinal axis such that the anterior curvature of the rod willroughly conform to the lateral curvature of the opening between theentry site and the medullary canal. As the surgeon pushes the rod intothe opening, progressive rotation of the rod about its longitudinal axisat the appropriate time, e.g. when the rod is inserted an appropriatedistance into the entry site, is guided preferably both by the spiralflutes and the curved portions of the IM rod. This rotation allows theanterior curvature of the rod to conform with the curvature of the longbone with a minimum of transverse point loading from the rod due to theinsertion procedure. If the curved portions of the rod were improperlyplaced due to incorrect rotation of the rod, the curved sections couldpotentially apply loads against the side of the bone leading tosecondary fractures of the bone. Finally, as insertion nears completion,the curved segments of the rod located closer to the proximal end of therod are rotated into their proper position within the bone andultimately align themselves within the bone opening.

As a result of the features of the preferred IM rod, the potential foriatrogenic fracturing of the long bone, such as for example the femur,is decreased because the surgeon is assisted in inserting a properlyshaped rod into the long bone (without applying adverse forces to thebone), with a precision that would be difficult to achieve with priorart IM rods. It is envisioned that these features, singularly or incombination, could also be adapted to any of the long bones (i.e.humerus, radius/ulna, femur, tibia/fibula) and to other types ofinternal fracture fixation devices to likewise ease their use.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed figures are for purposes of description and may illustratepreferred features of the IM rod which may be optional, and whichfurther may be combined or used singularly. These figures are intendedto be illustrative only and in no way serve to limit the scope of theinvention. The present invention is limited only by the claims.

FIG. 1 is a profile view of a preferred embodiment of the intramedullaryrod with spiraling flutes.

FIG. 2 is a cross-sectional view of the intramedullary rod, through line2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of a portion of the intramedullary rod,through line 3-3 of FIG. 1, showing the various openings provided at thehead of the rod.

FIG. 4 illustrates the intramedullary rod of the present inventioninserted into a femur, with two cross-members extending through the rodand into the femoral head.

FIG. 5 illustrates the intramedullary rod of the present inventioninserted into a femur, with two cross-members extending from the greatertrochanter to the lesser trochanter.

FIG. 6 is a profile view of the intramedullary rod with spiraling flutesof the present invention, showing the curvatures located in thelateral-medial plane of the device.

FIG. 7 is a profile view of the intramedullary rod with spiraling flutesof the present invention, showing the curvatures located in theanterior-posterior plane of the device.

FIG. 8 is a cross-sectional view of an end cap.

FIG. 9 is an end view of an end cap.

FIG. 10 is a cross-sectional view of an alternative end cap.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show the preferred embodiment of the IM rod of the presentinvention which is designed for insertion into and for the treatment ofthe femur. Although the IM rod will be described for use in the femur,it will be appreciated that its features have application in IM rods forlong bones including the humerus, radius/ulna, femur, tibia/fibula, oreven other bones. The IM rod of the present invention is designed forthe treatment of a variety of fractures and preferably comprises acentral bore 102 extending the length of the intramedullary rod 100 withan opening 103 to the exterior at the head portion 105 and an opening101 to the exterior at the stem 108, creating a cannulated rod. Thecannulation allows the rod to be placed over a guide wire inserted intothe bone for guidance and alignment. Likewise, the cannulation of therod may be omitted if desired or appropriate, such as with a smallerdiameter or shorter length IM rod. The rod may be provided in varyinglengths and diameters to allow the surgeon to properly match the finaldimensions of the rod with the physical and medical characteristics ofthe patient being treated. The rod is preferably composed of abiologically non-reactive metal such as titanium or a metal alloy suchas a titanium alloy, other metals such as stainless steel or non-metalmaterials, although other materials could conceivably be used as well.

Preferably, the rod 100 may include transverse openings located in thelateral-medial plane of the IM rod as shown in FIG. 3. The head portion105 optionally may include transverse holes 120 and 121, a transversehole 130, and/or an elongated transverse hole 140. Each of theseopenings may have an axis which extends through the IM rod at an anglewhich produces fracture fixation characteristics desired by the surgeon.For example, transverse holes 120 and 121 are preferably oriented at anangle of between 35° and 75° from the longitudinal axis of the rod, andmost preferably at an angle of 66°. Transverse holes 120 and 121 mayhave parallel axes and may have equal diameter bores. Transverse hole130 is preferably oriented at an angle of 25° and 75° from thelongitudinal axis of the rod, and most preferably at an angle of 45°.Elongated transverse hole 140 is preferably oriented at an angle ofbetween 5° and 35° from the longitudinal axis of the rod, and mostpreferably at an angle of 16°. These transverse openings are sized toaccept cross-members such as, for example, screws or nails which engagethe bone tissue of the affected bone. For example, if a femoral neckfracture is being treated, one or more femoral neck screws 200, shown inFIG. 4, can be inserted through transverse holes 120 and 121, and theninto the head of the femur. Preferably, the femoral neck screws utilizedare 6.5 mm diameter titanium lag screws. Different size transverse holes120, 121 may be provided to accommodate different size cross-members.The first neck screw may also be a different size than the second neckscrew. The threaded ends 210 of the femoral neck screws may engage andsecure the femoral head, while the optional use of two of these screwsprevents rotation of the femoral head relative to the femur. It isenvisioned that other appropriate fixation cross-members known in theart such as nails, helical blades, tacks, bolts, pins or the like couldalso be utilized for securing the femoral head, as they could be for anyof the other fixation situations described herein.

In the treatment of femoral shaft fractures, locking screws can beinserted through transverse hole 130 and/or elongated hole 140, and theninto the lesser trochanter to provide stable fixation in both thelongitudinal direction and torsionally. The optional use of a singlelocking screw through elongated hole 140 allows the proximal portion ofthe femur to move in relation to the distal end of the rod, therebyproviding torsional fixation alone. Other fixation or anchoring memberssuch as nails (including those with helical blades), tacks, bolts, pins,etc. may be inserted through holes 130, 140.

The stem 108 of the rod preferably includes distal transverse holes 110,111 and 112. Distal holes 110 and 112 may be located in thelateral-medial plane of the IM rod. Distal hole 111 preferably isangularly offset by 25° about the longitudinal axis of the rod fromdistal holes 110 and 112. Locking screws can be inserted through thebone into distal hole 111, and into either or both distal holes 110, 112to lock the distal portion of the rod to the femur. By inserting thelocking screws in different planes, the rod can be secured to the bonewith greater stability. Other fixation or anchoring means such as nails(including those with helical blades), tacks, bolts, pins, etc. may beinserted through holes 110, 111, 112.

The stem 108 of the rod includes channel-like formations 104 with“flutes” 109 formed in between the channels 104 along the surface 106 ofthe stem 108. The flutes preferably extend from below the base of thehead portion 105 down to the distal end of the stem 108. Mostpreferably, the flutes 109 begin about 75 mm to 95 mm from the proximalend of the rod. Like flutes known in the art, flutes 109 providebenefits such as improved medullary revascularization, reduced stiffnesswith greater strength, and improved torsional fixation at the rod-boneinterface. In a preferred embodiment, as shown in FIG. 2, there are sixflutes 109 although more or less may be implemented. Flutes 109preferably do not extend down the stem of the rod in a straight pathparallel to the longitudinal axis 10 of the rod, but rather extend in aspiral or helical fashion down the length of the stem 108 as can be seenin FIG. 1. The flutes preferably rotate or twist through approximately90 degrees about the longitudinal axis 10 of the IM rod as they travelfrom their start point to their termination point. However, the amountof rotation may vary as desired. The direction of the rotation generallydepends upon whether the IM rod is being inserted into the left side orthe right side of the body because the IM rod is preferably rotated tothe rear of the patient. When viewing the rod from its proximal end toits distal end, the flutes will rotate counter-clockwise on the leftside rods and clockwise on the right side rods. Understandably, thedirection of rotation could vary depending on the use and structure ofthe IM rod.

The flutes 109 are preferably formed by milling the surface of the stemto form the spiraling flutes of the rod 100. However, the flutes 109could also be formed by other means known to those of skill in the art.In addition, other types of surface deformations or protrusions couldconceivably fulfill the role of flutes 109.

As the rod 100 is inserted through the entry site, preferably located atthe greater trochanter, offset from the piriformis fossa of the femur,and into the femoral canal, the flutes 109 tend to engage bone tissueand therefore guide the twisting motion of the rod. Unlike an IM rodwith straight flutes, which would impede the rotation of the rod duringinsertion, the spiral flutes 109 of the rod 100 actually assist intwisting the rod. Because the rate of rotation of the spiral about thelongitudinal axis is predetermined, the proper amount of rotation isapplied to the rod 100 as a function of the extent of insertion. Thisgreatly facilitates the proper insertion and final alignment of thecurved rod, and reduces the potential for inadvertent bone fracturingdue to either premature or delayed twisting of the rod 100. Also, bonetissue is spared from the cutting that would occur from twisting an IMrod with straight flutes.

Removal of the rod from the femur is also facilitated by the presence ofthe spiral flutes 109. During the healing process, bone ingrowth maycause the IM rod 100 to be tightly embedded within the medullary canal.The spiral flutes 109 facilitate removal by guiding the rotation of therod 100 as it is pulled from the medullary canal, applying theappropriate amount of twist to the rod so that the curved sections willapply reduced transverse pressure to the bone as the rod 100 is removed.

The rod 100 preferably has three curved sections 301, 302, 303 along itslength, preferably with two of the curves located in the same plane andthe third preferably located in an orthogonal plane, as shown in FIGS. 6and 7. The various curves in the rod are formed using a commerciallyavailable, computer controlled, bending machine capable of incorporatingthese complex curvatures into the rod 100. Other methods of creatingthese curved sections are known and may also be utilized in theconstruction of the device.

The first curved segment 301 preferably begins at the proximal head 105and preferably ends at a straight segment 304. Most preferably, thefirst curve 301 begins about 26 mm from the proximal end of the IM rodand is bent to about a 6.5° arc angle. The first curve 301 preferablyhas a radius of curvature R1 of between about 100 mm and about 500 mmand more preferably about 300 mm (approx. 11.8 inches). The first curvemay start at a different location, be bent to a different angle and mayhave a different radius of curvature. In addition, the radius ofcurvature R1 for the first curve 301 may vary over the length of thefirst curved segment. The first curved segment may have a length in oneembodiment from about 10 mm to about 60 mm and more preferably may beabout 34 mm for an IM rod intended to be inserted in the femur. Thelength of first curved segment 301 may be longer or shorter than thevalues recited above depending upon the design needs. When the rod 100is placed into its final position within the femur, the first curve 301lies in the lateral-medial plane of the femur and is directedtransversely away from the body, towards the entry site at the tip ofthe trochanter, as illustrated in FIGS. 4 and 5.

The second curved segment 302 lies in the same plane as the first curve301, but begins at a point beyond the termination of the first curve,preferably below the head 105 of the rod 100. Most preferably, thesecond curved segment 302 begins about 75 mm from the proximal end ofthe IM rod and is bent to about an 8.5 degree arc angle. A straightsegment 304 of the IM rod preferably separates first curved segment 301and second curved segment 302 from each other. The second curved segment302 preferably has a radius of curvature R2 of between about 100 mm andabout 1500 mm, and more preferably about 800 mm (approx. 31.5 inches).The second curved segment 302 may start at a different location and mayhave a different radius of curvature. In addition, the radius ofcurvature R2 for the second curved segment 302 may vary or change overthe length of the second curved segment 302. The second curved segment302 may have a length in one embodiment from about 10 mm to about 220mm, and more preferably may be about 120 mm in length for an IM rodintended to be inserted into the femur. The length of the second curvedsegment 302 may be more or less than the values recited above dependingupon the design needs.

The nature of the first and second curved segments 301, 302 is such thatthe IM rod preferably more properly conforms with the transition of thecavity formed in the bone that extends from the insertion point and intothe medullary canal than if the rod were merely straight. Accordingly,there is a reduction of unnecessary transverse loads acting on the bonefrom the intramedullary rod and this helps to reduce the risk of aninadvertent secondary fracture arising from the insertion or removalprocess.

As shown in FIG. 7, the third curved segment 303 preferably is between70°-120°, and more preferably orthogonal to the first and second curvedsegments 301, 302 and is preferably located in the anterior-posteriorplane to match the anterior curvature of the medullary canal.Preferably, the third curve 303 begins at a point along the stem 108 ofthe rod 100. Most preferably, the third curve 303 begins about 180 mmfrom the proximal end of the IM rod and continues to the end of the rod.The third curve preferably has a radius of curvature R3 of between about500 mm and about 2500 mm, and more preferably about 1000 mm (approx.39.4 inches). The third curve may start at a different location, or endat a different location, and may have a radius of curvature R3 that isdifferent than the values recited above. In addition, the radius ofcurvature R3 for the third curved segment 303 may vary or change overthe length of the third curved segment 303. The third curved segment 303may have a length in one embodiment from about 10 mm to the remaininglength of the IM rod. The length of the third curved segment 303 may bemore or less than the values recited above depending upon the designneeds.

The third curved segment 303 is formed in a manner that preferablyconforms with the natural curvature of the bone and therefore helps toreduce the risk of an inadvertent secondary fracture. The third curvedsegment 303 also preferably partially overlaps the second curved segment302 to form a co-planar curve that results in the rod 100 having a“twist” through this section. In other words the IM rod in thisoverlapping section 305 curves in two planes. Most preferably, thesecond curve 302 and the third curve 303 overlap each other byapproximately 20 mm, however, the amount of overlap could vary withinthe range of approximately 0 mm to the length of the IM rod. As with thespiral flutes 109, this twist assists in guiding the rotation of the rodabout its longitudinal axis as it is inserted into the medullary canal.The configuration of the twist results in the rotation of the rod in thesame direction of rotation that the spiral flutes rotate the IM rod.

In use, the surgeon chooses an appropriately sized FM rod 100 based uponthe patient's physical characteristics and medical condition. To assistin the insertion of both the IM rod 100 itself and the variouscross-members into proximal transverse holes 120, 121, 130 and 140 ofthe rod, a guide tool (not shown) in the form of an insertion handle ismounted to a hole 160, preferably threaded, located at the top of thehead portion 105 of the rod. A slot 170 is used to align the insertionhandle with the IM rod 100 about the longitudinal axis of the rod 100.Thus, when the IM rod 100 is within the medullary canal of the bone, theorientation of the rod 100 can be identified by the position of thehandle.

An osteotomy at the tip of the greater trochanter is made to create anentry site and a flexible reamer is used to create a cavity in themedullary canal. The surgeon then orients the IM rod 100 so that it isrotated 90 degrees about its longitudinal axis from its final position,thereby roughly orienting the anterior-posterior curvature of the rodwith the curved opening from the entry site to the medullary canal. Asthe surgeon pushes the stem of the IM rod 100 into the medullary canal,the spiral flutes 109 and the co-planar curvature of the rod help toguide the rotation of the IM rod 100 approximately 90 degrees so thatthe various curves conform with the opening through the bone.

Once the rod 100 is fully inserted into position within the bone, anaiming arm on the insertion handle is used to locate the transverseholes through the rod 100. Cross-members are aligned with theirrespective holes through the rod 100 and inserted into the bone andthrough the rod to fix the bone as required by the type of fracturebeing treated.

After insertion of the rod and cross-members, an end cap 400 (shown inFIG. 8) can be installed in the hole 160 to prevent bony ingrowth withinthe hole. End cap 400 is designed to be recessed within the head 105 ofthe rod 100 once installed, while an alternative end cap 500 (shown inFIG. 10) extends beyond the head 105 of the rod 100 to extend the rod'soverall length as desired. Both end caps are provided with sockets 410(shown in FIG. 9) for the insertion of an appropriate installation tool.

It will be appreciated that certain preferred embodiments and featuresof the IM rod have been described and illustrated, but numerousmodifications and other embodiments may be devised by those skilled inthe art. For example, although the IM rod has been described withreference to its use in the femur, the IM rod could be used in thetreatment of other long bones using some or all of the featuresdescribed herein with the size and shape optionally being changed. Thefeatures described herein may be used singularly or in combination.Therefore, it will be understood that the appended claims are intendedto cover all such modifications and embodiments which come within thespirit and scope of the present invention and the invention will bedefined by the claims given their broadest interpretation.

1-39. (canceled)
 40. A method for treating long bone fractures,comprising: creating an entry site into a medullary canal of a longbone, the entry site being laterally offset from a longitudinal axis ofthe medullary canal; positioning an intramedullary rod at an opening ofthe entry site in an initial position relative to the bone, theintramedullary rod extending along a rod longitudinal axis and includinga head, a stem and first, second and third curved segments, the firstand second curved segments curving relative to the rod longitudinal axisin a first plane and the third curved segment curving relative to therod longitudinal axis in a second plane; a plurality of spiral flutesextending along a portion of the stem; and inserting the intramedullaryrod into the medullary canal of the bone by moving the intramedullaryrod distally with respect to the bone, the spiral flutes rotating theintramedullary rod about the rod longitudinal axis as the intramedullaryrod is inserted distally into the bone so that the first and secondcurved segments conform to the opening of the entry site as theintramedullary rod is moved from the initial position to a desired finalposition within the medullary canal.
 41. The method of claim 40, whereinthe third curved segment corresponds to a curvature of the medullarycanal when the intramedullary rod is in the final position.
 42. Themethod of claim 40, further comprising inserting a fixation elementthrough a transverse opening extending through the intramedullary rod tofix the intramedullary rod relative to the bone.
 43. The method of claim40, further comprising creating a cavity through the medullary canal ofthe bone using a flexible reamer.
 44. The method of claim 40, whereinthe intramedullary rod is rotated approximately 90 from the initialposition to the final position.
 45. The method of claim 40, wherein theflutes spiral clockwise about the stem from distal to proximal so thatthe intramedullary rod is rotated clockwise during insertion into themedullary canal.
 46. The method of claim 40, wherein the flutes spiralclockwise about the stem from distal to proximal such that theintramedullary rod is rotated counter-clockwise during insertion intothe medullary canal.
 47. The method of claim 40, further comprisingcoupling an end cap to a proximal end of the intramedullary rod toprevent bony ingrowth therein.
 48. The method of claim 40, wherein thefirst curved segment is separated from the second curved segment by asubstantially straight extending section therebewteen.
 49. The method ofclaim 41, wherein one of the first and second curved segments overlapsthe third curved segment along the longitudinal axis of theintramedullary rod.
 50. The method of claim 40, wherein the flutes areformed as spiral projections from an external surface of a portion ofthe stem.
 51. The method of claim 40, wherein the intramedullary nailfurther includes a spiral channel formed between adjacent flutes. 52.The method of claim 40, wherein the first curved segment is between 10mm and 60 mm in length.
 53. The method of claim 40, wherein the secondcurved segment is between 10 mm and 220 mm in length.
 54. The method ofclaim 40, wherein the first segment has a first radius of curvature andthe second curved segment has a second radius of curvature, the firstradius of curvature being different than the second radius of curvature.55. The method of claim 54, wherein the second radius of curvature islarger than the first radius of curvature.
 56. The method of claim 54,wherein the first radius of curvature is between 100 mm and 500 mm andthe second radius of curvature is between 100 mm and 1500 mm.
 57. Themethod of claim 41, wherein the third curved segment has a third radiusof curvature between 500 mm and 2500 mm.
 58. The method of claim 40,wherein each of the first and second curved segments has a correspondingcenter of curvature, both centers of curvature being located on the sameside of the longitudinal axis in the first plane.
 59. The method ofclaim 42, wherein the transverse opening extends through the nail at anangle with respect to the rod longitudinal axis.